The aluminium nitride has been known to have the high thermal conductivity and employing this property, a sintered body of aluminium nitride is available as a ceramics. And, the aluminium nitride powder has been proposed to use as a filler for encapsulating material for IC and a filler for a synthetic resin or rubber admixture, including an adhesive.
While, the aluminium nitride has the property of easily reacting with water, thereby it being easily hydrolyzed to decompose into a hydrated alumina with the production of ammonia. Because of this property, the following problems are caused.
(a) When the aluminium nitride powder is shaped by slip casting, tape casting etc. and then sintered so as to prepare the sintered body, water cannot be used as a shaping medium. Therefore, the shaping methods should be limited and the organic solvent should be used as the shaping medium. For this, the production cost is higher and the danger of explosion may occur.
If water is used as the shaping medium, the sintered body having the desired thermal conductivity cannot be obtained because the oxygen content in the aluminium nitride powder remarkably increases by the reaction with water.
(b) The aluminium nitride powder should be stored under the severe conditions because it is readily subjected to the hydrolysis by the moisture in the atmosphere. If the aluminium nitride powder is stored under the unsuitable conditions, therefore, the oxygen content therein may progressively and remarkably increase.
When the aluminium nitride powder is used as the filler, the quality of the filler may be impaired during the storage and usage.
As the method for solving these problems, the method for improving the water-resistance of the aluminium nitride powder was proposed. This method comprises heating the aluminium nitride powder at about 600 to 800.degree. C. to form the aluminium oxide coatings on the surface of each particle. However, the water-resistance of the aluminium nitride powder cannot be stably kept for a long period.
An object of the present invention is to provide the aluminium nitride powder having the stable water resistance for a long period.
An other object of the present invention is to provide the aluminium nitride powder which is suitable as the starting material for preparing the sintered body of aluminium nitride.
A further object of the present invention is to provide the aluminium nitride powder which is suitable as the filler for encapsulating material for IC and the filler for the synthetic resin or rubber admixture.
A further object of the present invention is to provide a method for treating the aluminium nitride powder so as to improve its water-resistance.